Introduction: Mental retardation is one of the most important problems of general health. The purpose of this study was to evaluate inheritance pattern of mentally retarded patients in Yazd city.
Methods: In a descriptive cross- sectional study, all medical records and pedigrees of 320 mentally retarded children whose parents had referred for genetic consultation to the Welfare center of Yazd city were reviewed.
Results: Of the total, 62.8% of the parents had consanguineous marriage. Mean inbreeding coefficient of offsprings was 0.0713 in third degree related parents versus 0.0156 in non-related parents. Mental retardation was seen in 43.4% of first– degree relatives of children (6.6% of parents and 36.8% of siblings, respectively). Frequency of mental retardation did not differ significantly in both sexes. Pedigree showed inheritance pattern in 43.4% of patients (autosomal recessive, autosomal dominant and x-linked inheritance pattern were seen in 33.75%, 6.9% and 2.8%, respectively), while 37% of patients had no definite inheritance pattern. Abnormal karyotype were seen in 19.4% of patients, 28 of whom(8.75% of all patients) had Down syndrome. The prevalence of autosomal recessive inheritance in patients with consanguineous marriages and non family marriages was 62.8 % and 10%, respectively (P=0. 002).
Conclusion: Since multiple cases of mental retardation were seen in families and rate of consanguineous marriage was more in parents of mentally retarded children, genetic counseling in consanguinity marriages and families of mentally retarded children can prevent incidence of mental retardation in these families.